GONYEA: The movie "Lincoln" documented the U.S. House passage of that constitutional amendment, which abolished slavery. That was in January of 1865. There was still one more step, though. To make it law, 27 states would have to approve the amendment.

(SOUNDBITE OF MOVIE, "LINCOLN")

DANIEL DAY-LEWIS: (as Abraham Lincoln) The Northern states will ratify, most of them. As I figure, it remains for two of the Southern states to do the same, even after all are readmitted. And I've been working on that. Slavery, sir - it's done.

GONYEA: One of the millions of people to see the movie was Ranjan Batra, a doctor in Jackson, Mississippi.

DR. RANJAN BATRA: I was curious when he said that. So, when I went home that evening, I picked up my laptop and started looking around.

GONYEA: Of all the 36 states in the Union at the time, only four voted against ratifying the amendment: Delaware, New Jersey, Kentucky and Mississippi. All four of them eventually did get around to voting for ratification. By far, the last though, was Mississippi. It didn't ratify the 13th Amendment until 1995. But that wasn't the end of the story.

BATRA: There, there was an asterisk against Mississippi and the little footnote said that although Mississippi had voted to ratify it, that ratification was not official because it had never been reported officially to the National Archives.

GONYEA: In other words, because nobody filed the paperwork in 1995, Mississippi technically never ratified the 13th Amendment. For Mississippi, it was only symbolic. But still, Dr. Batra thought...

BATRA: This is something that really should be fixed.

GONYEA: Ranjan Batra doesn't have too many political connections in Jackson, but he had a friend down the hall at the University of Mississippi Medical Center named Ken Dale Sullivan. Ken knew who to call. Plus, this meant a lot to him personally.

DR. KEN DALE SULLIVAN: My father was in Mississippi as a young man in his early twenties, when the first Freedom Riders came into Jackson. And he saw them arrested and put on buses. And I've heard these stories and I've heard the struggles. And people need to know that it happened, but they need to know that Mississippi has moved forward so much.

GONYEA: So, Sullivan got an appointment with Delbert Hosemann, the secretary of state in Mississippi. His office took things very seriously, Sullivan says.

SULLIVAN: And towards the end of January, they called and said they had the documentation ready to transmit to the Archives.

GONYEA: A couple weeks passed. Then one day earlier this month Sullivan received a letter from the Federal Register.

SULLIVAN: And the last paragraph of that letter said: With this action, the state of Mississippi has successfully ratified the 13th Amendment to the Constitution of the United States.

GONYEA: A mere 148 years later, all 36 states that were then in the Union have now ratified the 13th Amendment. And the most fitting detail of all? That confirmation letter arrived on February 12th, the birthday of one Abraham Lincoln.